This invention pertains to a method of ink jet printing, in particular to a method of ink jet printing with an ink set comprising a gloss equalizing colorless ink.
For photographic and other high definition imaging, uniform, high gloss is desirable to enhance the perception of clarity and sharpness of image. Ink jet printers can be used to print digital images with photographic quality if a suitable recording medium, such as glossy ink jet paper, is used. This paper is coated with an ink jet ink receptive layer to carry the image and absorb vehicle (reduce dry time).
Two types of ink jet receptive coating structures are commonly used for ink jet photo glossy media: swellable-polymer, non-porous media (“polymer” media) and a microporous, porous media (“microporous” media). A third type, often referred to as hybrid ink jet media, makes use of a combination of these coating technologies. The coatings are applied to a substrate such as a cellulose-based sheet or PET film.
The polymer-coated media typically comprises a hydrophilic polymer that absorbs the aqueous vehicle, dries the ink, and binds the colorant to the media. Typical polymers for this application are polyvinyl alcohol (PVA) and polyvinylpyrrolidones (PVP). The advantages of polymer coating are high gloss (typically 60 to 90 gloss units, GU, measured at 60°) and a relatively large capacity for aqueous vehicle absorption. The disadvantages are slow dry times and poor durability, in particular poor waterfastness.
The microporous media are typically comprised of water-absorbing fine particles or powders mixed with a polymeric hydrophilic binder to form a microporous structured coating. The hydrophilic particles or powders are typically polycrystalline inorganic materials such as boehmite alumina or amorphous inorganic materials such as aluminum silicates. In some cases, hydrophilic polymeric spheres, such as polyacrylic acid or latices, are the hydrophilic particles. The advantages of microporous media are quick drying and improved durability, in particular waterfastness and smudge resistance. The disadvantages are low gloss (typically less than 60 GU at 60°).
As ink jet printing speeds increase, microporous photo glossy papers are preferred due to their quick drying capabilities and improved durability.
It is difficult to achieve uniform gloss with most ink/media combinations because the ink tends to cause a change in gloss relative to the unprinted media. The effect increases with increasing color density (i.e. tonal value) and is particularly evident when printing with pigmented inks. There is need for a simple means to achieve uniform gloss between the medium (no ink) and the printed areas (all color densities, all colors) with any ink set.
U.S. Pat. No. 5,972,089 teaches use of phosphated esters in colored inks to increase gloss a high coverage.
U.S. Pat. No. 6,209,998 teaches application of heat to an image printed with pigment ink so as to smooth out the surface of the print and thereby increase gloss.
EP-A-1145865 provides a coating liquid for forming a transparent top coat on a image imparting light resistance, water resistance, fixation and glossiness.
JP-A-08085218 appears to describe the use of combinations of colored and colorless inks to print on transparent base material. The colorless ink should have at most a 0.1 difference in refractive index from the colored inks.
WO02/087886 appears to describe ink jet printing with combinations of colored and colorless inks to obtain a practically uniform glossiness.
All of the above publications are incorporated by reference herein for all purposes as if fully set forth.